1. Field of the Invention
The present invention relates to a displacement measuring apparatus and a velocity measuring apparatus which perform noncontact measurements of a displacement amount and a velocity, respectively.
2. Description of the Related Art
As a method of performing noncontact detection of a displacement amount of a moving object, the following two methods are known. One is a method of irradiating coherent light onto the moving object to generate a speckle pattern caused by a complex interference of luminous flux that is obtained by the reflection and the divergence of the light to detect a displacement or a velocity of the moving object based on a movement of the speckle pattern in accordance with a movement of the moving object. The other is a method of irradiating coherent light beams at incident angles different from each other with respect to the moving object to obtain a velocity of the moving object based on a difference between optical frequency Doppler shifts that are received at the time of the reflection and the divergence. However, in the methods described above, there is a problem of low reliability of an LD (laser diode) or a VCSEL (vertical cavity surface emitting laser) used as a coherent light source, high cost caused by the complexity of the configuration of an apparatus, or the like. Therefore, Japanese Patent Laid-Open No. 58-113762 discloses a method of using an incoherent light source to detect a displacement amount and a velocity of an imaged object.
However, in the velocity measuring apparatus disclosed in Japanese Patent Laid-Open No. 58-113762, an optical pattern image on a light receiving portion is not clear because reflected light from a surface of the moving object does not pass through an imaging system. Therefore, amplitude of a signal detected by a photo diode array of the light receiving portion is low, and an SN (signal to noise) ratio as signal integrity is deteriorated. As a result, detection accuracy of the displacement amount of the optical pattern image is reduced and measurement accuracy of the velocity is also reduced. On the other hand, if an imaging system such as a lens is added to the measurement apparatus in order to make the optical pattern image clear, the cost increases or reducing the size of the apparatus is prevented because of the increase of the number of the parts.